I will be changing my CU soon (from old 5-way fuse box). It is covered by my extension work on full plans. A few questions:
I currently pay British Gas for my electricity. If I want someone to come and upgrade from 60A to 100A and fit a breaker, do I contact my supplier (BG) or the infrastructure poeple (e-on in Midlands ?) Likely cost ?
The main fuse is in a brown plastic box with a slide-out section with finger grips on it. What will be the design of this (so I know the mechanics if I decide to pull it myself) ? Is it a captive fuse that will be pulled out when I pull out the sliding section ? How hard should I have to pull ? Is the fuse itself just like a very large cartridge fuse ? Any pictures ?
If I find an RCD is tripping all the time on some circuit having installed the new CU, can you get a slot-in "normal fuse" to use temporarily until you have time to investigate and fix ?
I'll probably get 16-way split unit. Any preferred makes ?
Anything special / funny needed for 17th Ed wiring ? I've got the onsite guide on order !
sm_jamieson coughed up some electrons that declared:
I believe the supplier is usually the place to start (BG). They will liase with the meter operator and the network operator as appropriate.
Good move to request an isolator.
If it's old, I would think twice about pulling it. The old stuff has occasionally been known to break apart in the hands, or the cable, if old paper insulated, to go bang if disturbed (in a visit to hospital sort of way - there be 300A or 500A fuses upstream in many cases).
Technically it's illegal to interfere with the cutout and meter but many do pull the fuse, especially if the seal's missing. If in any doubt about the state of the equipment, "don't" would be my advice. The guy from the "board" will have been trained to handle old crap and will have the necessary protective clothing required to do it safely.
If you're using RCBOs, swap for an MCB from the same maker. If using a split way board, the so called "17th Edition" boards have typically 3 busbars: 2 with RCD protection and one direct to the isolator. Spare MCB on the unprotected busbar should do it.
Hager, Contactum, MK Sentry, Wylex, Eaton/MEM, Square-D. I don't have personal experience of all of those but they're generally decent makes. Pros and cons of course and prices vary.
Square-D (owned by Schneider Electric who are good) have an interesting feature in that the busbar is fully shrouded and hidden round the back of the devices.
Major changes from the 16th:
RCD protection (30mA) required on:
a) All sockets (you may leave a couple out for fridge and freezer, sockets must be marked)
b) All circuits to a location containing a bath or shower, even the feed to the SELV transformer for any low voltage lights. This includes bedrooms with en-suites. Sockets (except shaver sockets) > 3m from zone 1.
c) In practise all circuits need RCD protection anyway, unless they are buried >50mm or mechanically protected in other (specific and approved) ways.
and
d) Zones in bathrooms changed - no zone 3 anymore.
e) Volt drops on final circuits used to be 4% of nominal (230V). It's now 3% for lighting and 5% for everything else. Unlikely to be a problem.
sm_jamieson coughed up some electrons that declared:
Almost: One of the better ways is to do something like:
RCD1 GF lights, FF sockets
RCD2 FF lights, GF sockets
Then split the rest of the load between the two.
The idea is that a fault caused by running a device plugged in doesn't plunge you into darkness. It plunges the person on the other floor into darkness instead. Again, no hard and fast answers - and personal circumstances might sway the descision.
Should be no difference in reliability. 2 RCDs is the practical minimum. All RCBOs obviously segregates faults better. The other aspect, is if you have a lot of equipment which is leaky due to mains filters or otherwise (eg refridgeration, computers) then with RCBOs you get more budget per circuit.
Anyway, it's an issue with no absolute right answer. I'm putting in all RCBOs, but the extra money is tiny compared to the budget for the whole renovation project.
If you have space to mount both CU's, then you can temporarily wire the new one from a spare high current way in the old one. Then you can try each of the circuits on the new CU and fix any such RCD issues. Depending on your total loading, you could leave some or all the circuits on the new CU (might have to leave a cooker and/or shower behind), and then have the tails moved across when you already know all the circuits work.
sm_jamieson coughed up some electrons that declared:
Generally they do, thing to look for is: is the CU capable of taking RCBOs (they are much taller than MCBs, unless they are double width types). If so, MCBs from either part or all of the manufacturer's range will fit.
Generally the more domestic kit (as opposed to industrial) have a range of MCBS, RCBOs, Dp isolator, RCCBs that are compatible with the current range of CUs by the same maker. Most manufacturers have downloadable brochures and datasheets, but if you were to buy from the local wholesaler, then select your CU and give them a list of the MCBs and RCBO by characteristic and they should be able to furnish you with a kit of parts that work.
No. Even if they fit, you've ruined any notion of the CU being "type tested" which means if it goes bang, overheats or otherwise fails, it's your fault.
Any comments on the following, a list of circuits for my CU replacement. It seems that even a 16-slot would be too small, given the amount of slots used by two double-pole RCDs and another double-pole switch for the non-RCD bus. Proposed CU circuits:
lights downstairs lights 1st floor lights loft sockets downstairs (not kitchen) sockets 1st floor sockets loft sockets kitchen ring (RCD) sockets kitchen radial (non-RCD / fridge) sockets kitchen cooker (30A ?) lights outside sockets outside power to garage / shed (mini-CU in there eventually) electric shower light in meter cupboard
These seem like logical groupings. How do folks manage with less ? How should I combine these ?
sm_jamieson coughed up some electrons that declared:
OK
I'd combine these, unless you're planning to run 500W in the loft or are concerned about the 1st floor and loft going dark at the same time?? Is it likely?
Good idea
OK
Combine with 1st floor ring?
Good idea, big loads in the kitchen
OK - but you need to mark the sockets as such AND protect the cable, which means:
MICC (aka "pyro", not practical unless you can do the terminations)
SWA Armoured (Bit excessive but fairly practical if all else fails, not actually as stupid as it sounds)
Steel conduit (yuk, bending and threading will be hard work) (metal capping is NOT acceptable),
Earth-foil-screen cable (there's a BS, can look up, but eg: Flexishield, X-Shield, and others - has caveats but probably easy to work with and practical. Difficult to buy and expensive. RS sometimes have it if you buy an entire drum.
Or run the cable on the surface and/or >50mm below wall/ceiling/floor surfaces. Mini trunking is acceptable.
Do you mean a cooker circuit? Depending on wheather this has an integral 13A socket, fusing could vary from 32A to 45A. Best size the cable for 45A and put a breaker in to suit your cooker.
Good idea
Ditto
Yep
Yes
Given you could run the cable on the surface here, thus not need an RCD, MCBs are cheap as chips, so why not? I see why you think this is a good idea. Other option is emergency light fitting which works in a power cut too.
Sure there'll be some different opinions. I've tried to explain why I'm made my statements, but again, it's not hard and fast.
2. The main fuse is in a brown plastic box with a slide-out section
It will probably be a captive large cartridge fuse that stays in the bit you pull. This will normally have "fingers" on it that connect to the fuse and poke into the bit fixed to the wall. To pull it you usually remove any wire seals if there are any, cut any paper ones, grab by the finger grips and pull[1]. The amount of pull required will normally be no more than that required to withdraw a plug from a socket.
There is one example here:
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that one the whole front bit come off revealing the terminals for both ends of the fuse, slight shrouded (but on that one, you could poke a finger into the live end if you wanted!). Normally with these I cover the live end with some tape as a precaution against something accidentally getting poked in there when working near it.
[1] Make sure there is no electrical load on the fuse when you pull it - e.g. turn the main switch off on the CU.
Normally when they say 16 way, that is the number of free ways with the RCDs/Switch in place. So if the board is a three way split with some switch ways and two lots of RCD protected ways, then the 16 ways will be over and above the six occupied by the switch and pair of RCDs.
If "loft" is just a loft, then no need for a separate circuit. If its a converted loft with several rooms, then that is different.
see comment above/
Did you mean "sockets" there?
These would be better of on RCBOs in the non RCD section of the board, or on their own RCD if you have more splits.
A "maintained" emergency light hooked up to whatever circuit illuminates the floor nearest the CU works well here. You can use it with a switch to light the cupboard for day to day stuff, but if the power to the circuit is interrupted then it will light from batteries. It makes finding a CU in the dark to reset a trip much simpler.
yup
Older installs may only have up and downstairs sockets - no kitchen etc. Might even only have a single socket circuit etc.
There are lots of ways, you need to think about how you are going to use the system, and what the implications of trips will be.
Hey, fantastic. If that 15-way CU won't do nothing will. The PDF doc available is also very useful. Now just to decide the ratings for each circuit etc.
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